Such a tap changer is known from WO 97/05536 [U.S. Pat. No. 5,969,511). In this known tap changer two load branches connectable with the respective winding taps are provided, wherein each of the two load branches is connectable by the semiconductor switching elements and can be electrically connected with a common load shunt. By contrast to usual tap changers with mechanical contacts for load switching or also the tap changer with vacuum switching cells for load switching, the known tap changer with semiconductor switching elements does not require any switch-over resistances
It is disadvantageous with this known tap changer that electronic power semiconductor switching elements are constantly loaded, even in unchanging operation, by the tap voltage.
It is the object of the invention to eliminate this disadvantage in the case of a tap changer according to category and to indicate a solution in which the electronic power components are cleared in unchanging operation.
A tap changer with a thyristor pair is, in fact, already known from WO 88/10502 [U.S. Pat. No. 5,006,784] in which in unchanging operation the current feed is taken over by a mechanical permanent main contact. However, this solution concerns a so-termed hybrid switch with a separate load changeover switch with numerous mechanical contacts, in which with use of a force store a rapid switching between the two winding taps of the tapped transformer is realized by means of a switch-over resistance that can be temporarily switched on. In the case of the invention, thereagainst, there shall be no need at all for switch-over resistances.